Various forms of video compression have been devised to compress motion video for storage and/or transmission, including various versions of the Motion Picture Experts Group (MPEG) specification promulgated by the International Organization for Standardization of Geneva, Switzerland, and the H.26x series of specifications promulgated by the International Telegraph Union (ITU) also of Geneva, Switzerland. Such forms of video compression employ lossy techniques that take advantage of various characteristics commonly observed in many pieces of motion video and of various limitations of the human visual system (HVS).
Among those techniques is quantization of blocks of coefficients of each frame of a motion video in the frequency domain to remove higher frequency components that are less perceptible to the HVS, and are therefore less likely to be missed during video playback. The extent to which higher frequency components are removed is usually controllable via one or more quantization parameters (QPs), and thus provides a mechanism by which a tradeoff between image quality and the data size of each frame of a motion video may be selected. As familiar to those skilled in the art, there is no single ideal QP setting that can be applied across all motion videos, or even through the entire length of most motion videos. Depending on the content of a portion of a motion video (e.g., colors, lighting, intricacies of patterns, extent and direction of movement, etc.), a selected QP value may cause one portion of a motion video to be perceived as having good image quality while also causing another portion of the same motion video to be perceived as having poor image quality.
It has become commonplace, during compression of a motion video, to evaluate the resulting image quality per compressed frame as an input to dynamically adjusting one or more QPs to at least prevent image quality from falling below a predetermined level. This is done even where the motion video is desired to be compressed relatively aggressively to cause its compressed form to fit within a relatively restrictive predetermined bit rate for transmission or overall data size for storage. Unfortunately, typical evaluation techniques tend to take into account only characteristics of the compressed frames of video, and do not take into account differences in the conditions under which the compressed motion video will ultimately be decompressed and viewed.